On Sun, 04 Jan 2004 19:35:50 GMT, "Form@C" wrote:

On Sun, 04 Jan 2004 17:17:32 +0000, Stewart Pinkerton wrote:

On Sun, 04 Jan 2004 08:27:50 GMT, "Form@C" wrote:

Have a look at any mid-price, fairly sensitive, half-decent speakers &
couple them with a little pure class A amp. Valves are nice...

No, they aren't - if you want *accurate* reproduction.


Maybe not, but do you want *accurate* reproduction or an amp that is good
to listen to? I, personally, would much rather listen to 2nd harmonic
distortion rather than 3rd!

Of course, the nice thing about SS amps is that you don''t have to
listen to either!

In any case,
how close would you be sitting to the orchestra to reach the dB level
for "several hundred watts" *at your seat*?

That's typically 100-105dB, so it depends on your room and your
speakers.

So, given fairly inefficient speakers of about 60dB/W you *need* less than
2W to reach that SPL. Double it to add some headroom. Say 5W. Even small
bookshelf speakers can be about 90dB/W, so this is loud.

Um, something wrong with your sums there, dude! with 90dB/w/m speakers
(which are well above the 86dB average), you will need 20 watts to
reach 103dB at one metre, which usually translates to 20 watts/channel
for the same level at the listening position in a small/medium room.
With 60dB/w/m speakers, you'd need a humungous 20,000 watts! Luckily,
I don't know of anything lower than 80dB/w/m (ATC SCM10s).

Remember to take the sqrt of the
power each time you double the distance back. You tend to sit far closer
to speakers than you do to the orchestra in a concert hall.

And the square law no longer applies once you are half way down the
room..................

No, it tends to get worse because of sound absorbtion (although there is
some reflected stuff too), so the SPL at your listening position is
probably less...

No no, it gets *better* because you are in the reverberant far field.
As noted above, in most small/medium rooms you'll get the dB/w/m
figure from a stereo pair at say 2 to 2.5 metres listening distance.

Try it. Use a
*good* low power amp and sensitive speakers. It's no use turning down a
100-200W monster amp because you arn't running them at their best. They
will be set up, probably anyway, to sound best at about 25-50% of full
output.

Absolute garbage!

Maybe for your amp... :-)

For any well-designed amp.

Remember that to double the volume you have
to square the power,

No, you need ten times the power.

Sorry, my mistake! I got carried away with sqrts....

so 250W is about twice the volume of a 25W amp, which in turn is
about twice the volume of a 5W amp! The more sensitive your speakers
are, the better.

Yes, but you still need good amplifier power to ensure adequate headroom
for peaks.

If you put an orchestral peak at, say, 200dB (way too high, I know - it
would deafen the conductor.), the SPL at your listening position at, say,
197dB (lost half of it) and your speaker efficiency at, say, 60dB/w
(fairly poor sealed boxes) then you need 4W to hit the peak volume. A 5W
amp is overkill. :-)

You really do need to read up on those sums! SPL is *logarithmic*, so
for every 10dB, you need ten times as much power. If you really had
60dB/w/m speakers, you would need 50 million *megawatts*!! That might
put a bit of a dent in your electricity bill..............

BTW, 200dB is about what you'd experience if a cruise missile went off
between your ears...................
--

Stewart Pinkerton | Music is Art - Audio is Engineering